EAST RUTHERFORD — Mario Manningham attended his first NFL training camp in 2008 as a third-round draft pick of the Giants, basically secured of his place on the team’s opening day roster.

Six years later, Manningham is back in Giants camp after a two-year, injury-plagued stint with the San Francisco 49ers. This time, Manningham is still recovering from offseason knee surgery, his third in three years, so there’s no guarantee of him being with the team when the season kicks off against the Detroit Lions on Sept. 8.

Manningham’s last knee surgery has prevented him from participating in any full drills as the Giants began their second week of training camp Monday. He has not been cleared by the team’s medical staff to resume football activities, so he falls behind on the team’s depth chart for every practice and preseason game he misses.

“I don’t have anything made here,” Manningham said Monday before the Giants took the field for their two-hour practice session. “I have to be here like I have something to prove. I can’t worry about what has happened in the past. That’s wasted energy. It’s a new team, with new faces and a new coaching staff. I have to try to get out there and prove what I can do.”

Manningham was one of the stars of the Giants’ last Super Bowl victory, making an acrobatic 38-yard catch down the sidelines on third down to keep the game-winning touchdown drive alive in the 21-17 win over the New England Patriots on Feb. 5, 2012.

Manningham had his best season as a professional with the Giants in 2010, catching 60 passes for 944 yards and nine touchdowns.

After that Super Bowl-winning season, Manningham became a free agent and signed with the 49ers, but never reached the same heights he achieved with the Giants. He caught only 42 passes and one touchdown in 2012, and had only nine catches for 85 yards and no scores last season. Both years were cut short by injury.

Manningham said he had no plans of returning to the team that drafted him out of the University of Michigan six years ago.

“I really didn’t think about it,” Manningham said. “I hit free agency and it just turned out this way. I settled back here.”

Manningham knows that the clock is ticking on his chances to make the Giants’ final roster.

“I know I still have to make the team,” Manningham said. “It’s frustrating not to be out there, but that’s just part of the game. I have a couple of cobwebs, but I’m getting there. I know my knee is fixed. It’s just my confidence, knowing whether I can stick my leg in the ground and turn the right away. Every day, it’s getting better and better.

“There’s not any pressure on me to get out there. But in the back of my mind, I know it’s up to me or them. I’m preparing myself to make the team.”

Giants quarterback Eli Manning is glad to have one of his former targets back.

“Mario enjoyed being a New York Giant and had a good thing going here,” Manning said. “Sometimes, you leave and you realize what you had. He left on good terms, went off, had some injuries and now he’s here. I’m glad to have him back.”

Same goes for wide receiving partner Victor Cruz.

“He was here when I was first coming through here,” Cruz said. “It’s a little nostalgic. He brings a lot of energy into the room again and it’s very beneficial for us.”

Manningham is not expected to see any preseason action until the fourth game in three weeks, giving him little time to make the final 53-man roster.

“This is still training camp,” said Manningham, who has caught 211 passes in his six-year career for 2,849 yards and 19 touchdowns. “You learn from mistakes. I just have to put myself in the best position to be on the field. I’m pretty close now.”

NOTES: New Giants QB coach Danny Langsdorf said that he would like to see Manning “around 70 percent” in his completion ratio this season, a number that Langsdorf realizes has only been reached nine times in the history of the league. “I want him to be able to spread the ball all over the field,” Langsdorf said. “But I also want him to be able to push the ball down the field in big chunks.” Manning has only reached 60 percent four times in his 10-year career, with a career best of 62.9 percent in 2010. His career percentage mark stands at 58.5 percent, after completing 57.5 last season.